During the production of engineered wood boards, in particular within the scope of a production method for floorboards, to which the invention also relates, a substrate in the form of a fibre mat is used, which contains wooden fibres and in particular is made from wood fibres and adhesive. A fluid is applied to this substrate, which is then pressed to form an engineered wood board. It is important for the fluid to be applied to the substrate as evenly as possible.
It is possible and represents a preferred embodiment that the application occurs as a spray. Up to now, the vapour resulting from this method has been analysed visually by directing light onto the vapour and observing the scattered light. This is comparatively complex and rather imprecise.
During the production process of floorboards, a fluid in the form of a fluid synthetic resin is also often applied to a substrate in the form of the engineered wood board; a paper layer is then laid on the engineered wood board and both are then pressed in a press under such pressure and at such a high temperature that the resin melts and solidly binds the paper layer with the engineered wood board. Such a method and related device are described in WO 2016/078734 A1, which is incorporated by reference in its entirety. A solid bond between the paper layer and the engineered wood board is an important quality criteria as too weak a bond may lead to bubbles forming between the two. In order to avoid this, it is also vital during this stage in the method to ensure that an even a layer of fluid as possible is applied to the substrate.
US 2009/0188642/A1 describes how to measure the moisture in an engineered wood board using infra-red spectroscopy. This type of measurement is always local and is therefore not able to record small-scale inhomogeneities that may occur during application.
A spatially resolved, infra-red spectroscopic measurement of the content of powdery resin in a plant fibre board is described in JP 2015-169569.
A method is disclosed in WO 92/01540 in which a fluid is applied inhomogenously to a material that is to be hardened, and/or a temperature gradient is applied in order to compensate for the inhomogeneity during the hardening process using microwaves. The temperature is recorded with a thermographic camera and the moisture by means of absorption or reflectivity infra-red spectroscopy, which is complex and not particularly robust.